III-V semiconductors are compounds which contain at least one element from Group III of the periodic table and at least one other element from Group V of the periodic table.
Several methods are known for the preparation of III-V semiconductors for applications in solid state electronic devices. For example, many of the III-V semiconductors were first prepared by direct combination of the elements at high temperatures and high pressures. Other routes have been developed to provide purer products and to avoid the hazards associated with earlier routes. Chemical vapor deposition (CVD) or metal organic chemical vapor deposition (MOCVD) have been used to deposit the semiconductors on a heated substrate by contacting the substrate with a gas stream which contains volatile Group III and Group V compounds.
The bulk properties of semiconductors are the properties which are exploited in semiconductor applications such as diodes and transistors. However, it has recently been shown that small-particle semiconductors of many types (I-VI, II-VI, III-VI) exhibit interesting and potentially useful electronic and nonlinear optical effects. The most promising materials incorporating these small-particle semiconductors contain the semiconductor particles embedded in a rigid glass, polymer or glass/polymer matrix.
Several methods have been used to prepare small-particle semiconductors in rigid matrices. In one approach, Cd, S and Se have been added to the standard ingredients of normal glass to prepare CdS or CdS.sub.x Se.sub.1-x glass cutoff filters by standard melt procedures. Glasses of this type are commercially available as long-wavelength-pass optical filters with several values for x. Nonlinear optical effects have been reported in these glasses, but the high temperatures and strongly oxidizing conditions used to prepare these glasses preclude the use of this technique for III-V semiconductor compositions.
Mahler, Inorganic Chem., Vol. 27, Number 3, 1988, pp. 435-436, discloses additional preparative methods, including metathesis in microemulsion, gas-solid reactions on high surface area silica, synthesis within the channels of perfluorocarbon sulfonic acid membranes, and generation of semiconductor particles within polymer films. In particular, ethylene-15% methacrylic acid copolymer (E-MAA) was shown to provide good mechanical and optical properties and confer high kinetic stability on nanometer-sized semiconductor particles.
Rajh et al., Chemical Physics Letters, Vol. 143, No. 3, 1988, pp. 305-307, disclose a method for incorporating quantized particles of colloidal semiconductors in transparent silicate glasses by mixing aqueous colloidal dispersrons of the semiconductor with tetramethoxysilane (TMOS), accelerating the polymerization of the silicon alkoxide by the addition of NH.sub.4 OH, and drying the resulting gel over a period of months. They also disclose a method for producing colloidal glasses by first incorporating metal ions, and then, after drying to about one-half the original volume, adding the appropriate anions for precipitating the particles via gaseous H.sub.2 S or H.sub.2 Se.
Roy et al., in "Better Ceramics Through Chemistry", Materials Res. Soc. Symp., Vol. 32, Ed. J. C. Brinker, D. E. Clark, D. R. Ulrich, Elsevier, 1984, disclose the inclusion of CdS and AgX (X=Cl, Br, I) in sol-gel monoliths by mixing a tetraethoxysilane/ethanol solution with an aqueous solution of the heavy metal ion.
Kuczynski et al., J. Phys. Chem., Vol. 89, 1985, pp. 2720-2722, disclose the preparation of CdS in porous Vycor.RTM. glass by soaking cleaned porous glass in a CdCl.sub.2 solution, drying the glass under vacuum and then immersing the impregnated sample in a sodium sulfide solution.
Unfortunately, none of these methods is applicable to the preparation of III-V semiconductor/glass or III-V semiconductor/glass/polymer composites because III-V semiconductors are both more difficult to prepare than, for example, II-VI semiconductors and because III-V semiconductors decompose in aqueous solutions. Such composites are desirable because they are expected to exhibit interesting and useful electronic and nonlinear optical effects analogous to those demonstrated for other small-particle semiconductor composites. Embedding the III-V semiconductor particles in a rigid matrix of glass or glass and polymer would also prevent aggregation of the III-V particles.
The nonlinear optical properties of semiconductors such as degenerate four-wave mixing, optical bistability and phase conjugation have been reported (Rustagi et al., Optics Letters, Vol. 9, No. 8 (1984), pp. 344-346, and references therein). Rustagi et al. describe an experimental arrangement for measuring degenerate four-wave mixing of visible radiation in a borosilicate glass doped with mixed semiconductor, CdS.sub.x Se.sub.1-x.
It is the object of this invention to provide a chemically and mechanically stable dispersion of small III-V semiconductor particles in a rigid matrix. Appropriately made materials should have faster optical nonlinearity than bulk III-V semiconductors. Wavelength tuning can also be conveniently achieved by controlling the size and concentration of the III-V semiconductor clusters. It is a further object of this invention to provide a method for generating third order nonlinear optical effects.